As specified in LFD Art. 8.10.1, there are three criteria for determining the effective width of a concrete flange in compression for interior beams. The three criteria are:

Precast/Prestressed Girder exactly as stated above checks criteria 1 and 3. However, for criteria 2, it is divided into two sub-cases:

For beams with very stiff upper flanges, e.g., AASHTO Type IV beam, using the edge of the flange as the point to begin measuring six times the slab thickness seems reasonable. T.Y. Lin cites such an example in Reference 6. For relatively thin-flanged members, such as Type VI beams, it may not be reasonable; therefore, Case 2b was introduced. Precast/Prestressed Girder can handle the beam/slab configurations as shown in the figure below. For exterior girders, an effective overhanging flange width not to exceed one-twelfth of the span, six times the thickness of the slab, or one-half the clear distance to the next web (LFD Art. 8.10.1.2). Precast/Prestressed Girder conservatively applies these code provisions individually to each side of exterior girders.

Three Cases Addressed by Precast/Prestressed Girder for Computing Effective Width of Compression Flange